Now she’s doing those twisty ones that I’ve never been able to manage more than about three of.

“So… shall we go?” I say.

“Go where?” Jess says without missing a beat.

“To the gym! I thought you wanted to…” I trail off as she starts raising her legs off the ground too.

OK, now that’s just showing off.

“I don’t need to go anywhere. I can work out here.”

Here? Is she serious? But there aren’t any mirrors. There isn’t any MTV. There isn’t a juice bar.

My gaze falls on a snakelike scar at the top of Jess’s shin. I’m about to ask how she did it, when she catches me looking and flushes red.

Maybe she’s sensitive. I’d better not mention it.

“Don’t you need weights?” I say instead.

“I’ve got them.” She reaches in her rucksack and pulls out two old water bottles filled with sand.

Those are her weights?

“I wouldn’t go near a gym,” she says, starting to raise the bottles above her head. “Waste of money. Half the people who join gyms never go, anyway. They buy expensive outfits and never even wear them. What’s the point in that?”

“Oh, absolutely!” I say quickly. “I totally agree.”

Jess stops and adjusts her grip on one of the weights. Then her eye falls on the back of my leggings.

“What’s that?” she says.

“Er…” I reach round with my hand.

Damn. It’s the price tag hanging out.

“Er… nothing!” I say, hastily tucking it in. “I’ll just go and get some… weights of my own.”

As I return from the kitchen with two bottles of Evian, I can’t help feeling a bit disconcerted. This isn’t exactly what I had in mind. I’d pictured the two of us running effortlessly along on adjacent machines, with some upbeat song playing and the spotlights making our hair look all shiny.

Anyway, never mind.

“So… I’ll follow you, shall I?” I say, joining Jess on the carpet.

“I’m going on to some biceps work,” says Jess. “It’s pretty straightforward.” She starts raising her arms up and down, and I copy what she’s doing. God, she exercises quite fast, doesn’t she?

“Shall I put on some music?” I say after a few moments.

“I don’t need music,” says Jess.

“No. Neither do I,” I say quickly.

My arms are starting to ache. This can’t be good for them, surely. I glance at Jess, but she’s steadfastly pumping away. Casually I lean down, pretending to adjust my shoelace. Then suddenly I have a thought.

“I won’t be a moment,” I say, and hurry out to the kitchen again. A few moments later I’m back, holding two slim silver bottles.

“Here’s a health drink,” I say, proudly holding one out to Jess. “So you can rebalance.”

“So I can what?” Jess puts down her weights with a frown.

“It says it on the bottle, look,” I explain. “It has a unique blend of life-enhancing vitamins and herbs.”

Jess is scanning the label.

“It’s just sugar and water. Look. Water… glucose syrup…” She puts it down. “No, thanks.”

“But it’s got special properties!” I say in surprise. “It rebalances, revitalizes, and moisturizes your skin from the inside.”

“How does it do that?”

“I… don’t know.”

“How much is it?” Jess picks the bottle up again and looks at the price tag. “It’s £2.95!” She seems totally scandalized. “Three pounds for some sugar and water? You could buy a twenty-kilo sack of potatoes for that!”

“But… I don’t want a twenty-kilo sack of potatoes.”

“Then you should!” says Jess. “Potatoes are one of the most nutritious, cost-effective foods available.” She eyes me reprovingly. “People underestimate them. But did you know a potato in its skin has more vitamin C than an orange?”

“Er… no,” I say nervously. “No, I didn’t.”

“You could live off potatoes and milk.” She starts hefting her weights again. “You’d get practically every nutrient the body needs, just from those two.”

“Right!” I say. “That’s… really good! Er… I’ll just go and have a shower.”

As I close the door of the bedroom, I feel totally bewildered. What was all that about potatoes? I’m not even sure how we got onto the subject.

I head down the corridor and see Luke through the door of the study, getting something down from a shelf.